2000 ranger xlt, 4.0 v6. This has been happening for a few years now. at random times while driving the RPMs will jump up 600-1000 and stay there for approximately 15-30 seconds, and the truck gets noticeably louder and if it does it while I am stopping, it's not easy. I used to have a tempo and when I got a vacuum leak, it acted exactly the same, only it was constant, so I'm not sure what it could really be. I'm not sure what the fuel pump in these trucks is like, but i know some vehicles have a two speed fuel pump, so maybe if these have the same thing, it would seem as if it is kicking into the higher speed at random times. Has anyone else had this issue? What other things could it be? Thanks for any information!

Not the fuel pump. The ranger uses a variable voltage pump, not the old school 2 speed. Is your AC on? It will bump the rpm when the compressor kicks on, but usually not that much. It also might still be a vacuum leak, if it is on a system that is switched, only opening the valve on occasion, thus causing a rpm spike. I'm not that familiar with the 4.0, so I don't know anything more to point you towards.

i have the same truck you have. 2000 xlt with the 4.0. my truck would idle really high when i cranked it 2500 rpm, and then run down to about 300 rpm and the rpm would jump trying to keep the truck running. it got so bad that it shut off on me at traffic lights and i would have to ease onto the accelerator to get the rpm back up. i took it to ford and they said i had approx 15 codes come up and it turne out to be a melted fuse